As Merck Manual defines: Nephrotic syndrome is urinary excretion of greater than 3 g of protein/day due to a glomerular disorder. It is more common in children and has both primary and secondary causes. Diagnosis is by determination of urine protein/creatinine ratio in a random urine sample or measurement of urinary protein in a 24-h urine collection; cause is diagnosed based on history, physical examination, serologic testing, and renal biopsy. Prognosis and treatment vary by cause.
In easier terms Nephrotic syndromeis a nonspecific disorder in which the kidneys are damaged, causing them to leak large amounts of protein(proteinuria at least 3 grams per day) from the blood into the urine.
Nephrotic syndrome occurs at any age but is more prevalent in children, mostly between ages 1 ½ and 4 yr. At younger ages, boys are affected more often than girls, but both are affected equally at older ages.
Kidneys affected by Nephrotic syndrome have small pores in the podocytes, large enough to permit proteinuria (and subsequently hypoalbuminemia, because some of the protein albumin has gone from the blood to the urine) but not large enough to allow cells through hence no hematuria (blood in urine).

The causes of Nephrotic syndrome can be divided into
1) Primary
2) Secondary
Primary causes:The most common primary causes are.

• Minimal change disease
• Focal segmental glomerulosclerosis
• Membranous nephropathy

Secondary Causes: Secondary causes account for < 10% of childhood cases but > 50% of adult cases, most commonly the following:

• Diabetic nephropathy
• Preeclampsia

The early symptoms include

• Loss of appetite,
• A general feeling of illness (malaise),
• Puffy eyelids and tissue swelling from excess sodium and water retention,
• Abdominal pain,
• Wasting of muscles (atrophy),
• Frothy urine.

As the disease progresses the symptoms include

• Pitting edema over the legs.
• Fluid in the pleural cavity causing pleural effusion. More commonly associated with excess fluid is pulmonary edema.
• Ascites: Fluid in the peritoneal cavity.
• Anascara: Generalized oedema throughout the body.
• Most of the patients are normotensive but hypertension (rarely) may also occur.
• Anaemia
• Puffiness around the eyes, characteristically in the morning.
• Dyspnoea maybe present due to pleural effusion or due to diaphragmatic compression with ascitesWhat are the complications of Nephrotic Syndrome?
• Venous thrombosis
• Infection: due to leakage of immunoglobulins, encapsulated bacteria such as Haemophilusinfluenzae and Streptococcus pneumoniae can cause infection.
• Renal failure is due to hypovolemia.
• Pulmonary edema: again due to fluid leak, sometimes it leaks into lungs causing hypoxia and dyspnoea.
• Growth retardation: Causes of growth retardation are protein deficiency from the loss of protein in urine, anorexia (reduced protein intake), and steroid therapy (catabolism).
• Vitamin D deficiency
• Anaemia
• Hypocalcemia

A doctor bases the diagnosis of nephrotic syndrome on the symptoms, physical examination findings, and laboratory findings.

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